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Here is my helpers.c file, I have been scouring the message boards and nothing is making sense. I use the pset3 input of ./generate 1000 50 | ./find 127. I get a Didn't find needle in haystack message. Please help. I apologize for the poor format, this is my first time posting to stackexchange.

/**
 * helpers.c
 *
 * Computer Science 50
 * Problem Set 3
 *
 * Helper functions for Problem Set 3.
 */

#include <cs50.h>
#include "helpers.h"

bool BinarySearch(int key, int array[], int min, int max);
/**
 * Returns true if value is in array of n values, else false.
 */
bool search(int value, int values[], int n)
{
    return BinarySearch(value, values, n-n, n-1);

}

/**
 * Sorts array of n values.
 */
void sort(int values[], int n)
{
    int i, element, j;
    for(i=1;i <n;i++)
    {
        element = values[i];
        j=i;
        while (j > 0 && values[j-1] > element)
        {
            values[j]=values[j-1];
            j=j-1;
        }
        values[j]=element;

    }

    // TODO: implement an O(n^2) sorting algorithm
    return;
}

bool BinarySearch(int key, int array[], int min, int max)
{
   //find midpoint
    int midpoint = (max-min)/2;

// check if input is valid

    if(min > max || midpoint > max || midpoint < min) 
    {
        return false;
    }

    //check if midpoint=key
    if(array[midpoint]==key || array[min] == key||array[max]==key)
    {
        return true;
    }else if(array[midpoint] < key) // check if midpoint is larger than the key
    {
        BinarySearch(key, array, midpoint+1, max);
    }else if(array[midpoint] > key) //check if midpoint is larger than key
    {
        BinarySearch(key, array, min, midpoint -1);
    }
    return false;

}
3

When you call a recursive function, you actually need to deal with the return value of that function. You are currently just calling BinarySearch(key, array, min, midpoint-1) for example and then throwing away whatever value it returns.

Be sure to return BinarySearch(...) whenever you call it.

Also, look again at your int midpoint value. If, for example, your max is 10 and your min is 8, should your mid be (10-8)/2 = 1? That's outside the range of what you are searching. Shouldn't the mid be 9 in that case? Perhaps just a typo in your equation?

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  • Awesome! Applied both fixes and BOOM!!! Needle Found! – Ian Sullivan May 5 '16 at 0:45

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